Conventionally, a route search apparatus for searching for and displaying a carbon dioxide discharge minimum route between a start place and a destination that minimizes the discharge of the carbon dioxide based on map information and a carbon dioxide discharge data for each link in the route. The carbon dioxide discharge data for each is calculated based on an index that is derived from greenhouse gas measurement data as well as a travel time of each link and the map information, and is stored in a memory of the apparatus. The route search apparatus for searching for such a route is, for example, disclosed in Japanese patent document JP-A-2005-03823.
Further, a technique for estimating the carbon dioxide discharged from a travel of a vehicle based on a calculation of a fuel consumption of each link by an equation is disclosed in, for example, a non-patent document “Proceeding of Civil Engineering Society (No. 695/IV-54, 125-136, 2002.1).” The equation for the above calculation isFuel consumption Q=0.3T+0.028D+0.056AEE                 T: Travel time, D: Travel distance, AEE: Acceleration energy        
The apparatus disclosed in the above patent document calculates the carbon dioxide discharge amount for each link based on a travel speed in each link, and the travel speed in each link is calculated based on traffic information received through communication and a travel distance of each link derived from map information. That is, the carbon dioxide discharge amount calculated in the above patent document does not reflect an influence of a travel time, a travel distance and the like of each link, thereby leading to an inaccuracy of the calculation of the carbon dioxide discharge amount.
Therefore, the equation in the above non-patent document may be employed for quantitatively calculating the carbon dioxide discharge amount for each link. However, the equation does not consider an influence of a slope of the road, the calculation disclosed in the non-patent document does not yet achieve a sufficient calculation accuracy.